Synthesis and structural characterisation of primary amine adducts of gallane, RH2N·GaH3, and of their decomposition products, [RHNGaH2]n (R = Me, n = 3; R = tBu, n = 2)

Abstract

Primary amine–gallane adducts, RH₂N·GaH₃ [R = Me (1) and ^tBu (2)], have been isolated for the first time from the reaction of [RNH₃]Cl with LiGaH₄ in Et₂O solution at ca. 273 K and characterised by their vibrational and ¹H NMR spectra. The structures of single crystals, grown at low temperatures and determined by X-ray diffraction, reveal pseudo-polymeric arrays of RH₂N·GaH₃ molecules with Ga–N distances of 2.0424(18) and 2.058(5) Å for 1 and 2, respectively. The adducts decompose at or near ambient temperatures with the elimination of H₂ and formation of the corresponding monoalkylamido derivative [RHNGaH₂]_n. The crystal structures of these at 150 K consist of either [MeHNGaH₂]₃ molecules with a ‘skew-boat’ conformation for the cyclic Ga₃N₃ skeleton (3) or [^tBuHNGaH₂]₂ molecules with a four-membered Ga₂N₂ core (4), with Ga–N distances averaging 1.986(8) and 1.991(3) Å for 3 and 4, respectively. The crystalline solids 1, 3 and 4 feature intermolecular N–H⋯H–Ga interactions with H⋯H distances estimated to fall in the range 2.1–2.3 Å. The significance of these is discussed.